Diurnal Tides

• A single high tide and low tide each day is called a diurnal tide; these tides occur about 12 hours apart. Unlike semidiurnal tides, high and low diurnal tides do not vary much from one day to the next in terms of height. The northern parts of the Gulf of Mexico and parts of southeast Asia receive this type of tide, as well as a few other areas scattered around the globe.
  
  

Semidiurnal Tides

• The semidiurnal tide pattern results in a tide approximately every six hours--two high tides and two low tides each day. Successive high tides on a given day vary only slightly in height; the same with successive low tides. However, the height of the tides changes from one day to the next. The tides on the United States' Atlantic coast exemplify this type of tide; Europe also experiences semidiurnal tides.
  
  

Mixed Tides

• Areas that receive mixed tides have longer tide cycles than those receiving semidiurnal tides. Unlike diurnal and semidiurnal tides, successive high and low tides vary widely in height; one high tide may be much higher than a second high tide on the same day. Coasts with mixed tides can be dominated by semidiurnal or diurnal tides. The west coast of the United States and Canada receives mixed tides, as well as many islands in the Pacific.
  
  

Spring Tide and Neap Tides

• Spring tides occur twice a month during full moons and new moons due to the sun, the earth and the moon aligning. These tides are higher or lower than typical tides because of the combined gravitational forces of the sun and the moon. During quarter moons, the sun, the moon and the earth form a right angle so that the gravity of the sun and the moon are in opposition. This results in the high tides being lower than normal and the low tides being higher than normal. These tides are called neap tides.